"We are not testing and I don't think you see advanced nuclear countries around the world testing. And certainly, we don't encourage other states to do that," State Department spokesman Sean McCormack said.

"All of that understood, you know, India is a sovereign country," he told reporters when asked to comment on raging debate in India over whether it enjoyed the right to test nuclear weapons under the landmark US-India civilian nuclear energy deal.

Indian Prime Minister Manmohan Singh told parliament this week that the deal would not curb India's right to test nuclear weapons, saying New Delhi retained the "sovereign right to test and would do so if it is necessary in the national interest."

But the United States responded by saying that the nuclear deal's operating agreement contained provisions for "full termination" of all nuclear cooperation with India, as well as requiring the return of any items, including reprocessed fuel, covered in the pact, if India tested atomic weapons.

MPs from four Communist parties, who prop up Singh's government in parliament, joined opposition lawmakers in alleging that the prime minister gave false information about the deal.

Uproar in both the upper and lower houses of parliament forced its adjournment for the day on Thursday.

India conducted its first nuclear test in 1974, resulting in Washington immediately cutting off nuclear cooperation with the Asian giant.